Petrography and Petrogenetic History of a Quartz Monzonite Intrusive, Swisshelm Mountains, Cochise County, Arizona

Petrography and Petrogenetic History of a Quartz Monzonite Intrusive, Swisshelm Mountains, Cochise County, Arizona

Petrography and petrogenetic history of a quartz monzonite intrusive, Swisshelm Mountains, Cochise County, Arizona Item Type text; Thesis-Reproduction (electronic); maps Authors Diery, Hassan Deeb, 1934- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 07/10/2021 02:41:07 Link to Item http://hdl.handle.net/10150/551749 PETROGRAPHY AND PETROGENETIC HISTORY OF A QUARTZ MONZONITE INTRUSIVE, SWISSHELM MOUNTAINS, COCHISE COUNTY, ARIZONA by Hassan D. Diery A Thesis Submitted to the Faculty of the DEPARTMENT OF GEOLOGY In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 19 6 1; STATEMENT BY AUTHOR This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library© Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author. SIGNED: D APPROVAL BY THESIS DIRECTOR This thesis has been approved on the date shown below: R. L. DUBOIS Date Associate Professor of Geology ABSTRACT PETROGRAPHY AND PETROGENETIC HISTORY OF A QUARTZ MONZONITE INTRUSIVE, SWISS HELM MOUNTAINS, COCHISE COUNTY, ARIZONA by Hassan D. Diery Department of Geology University of Arizona Tucson, Arizona The Swisshelm Quartz Monzonite covers about two square miles on the western slope of the Swisshelm Mountains, Cochise County, Ari­ zona. Field observation and petrographic study indicate that the quartz monzonite was derived by differentiation and late-stage alkali metasomatism of probably a quartz dioritic magma rich in alkali and volatile constituents. The high concentration of the volatiles is believed to be of great importance in the development of the differ­ ent facies and rock types. Four different facies of the Swisshelm Quartz Monzonite have been distinguished as (1) the normal facies, (2) the altered facies, (3) the fine-grained facies, and (1*) the con­ tact facies. Also, several aplite dikes, local beryl-bearing pegma­ tite patches, and numerous quartz veins are present and attributed to iii iv late magmatic differentiation. Inclusions of an early and late mag­ matic facies are sparsely disseminated throughout the quartz monzon- ite. The Swisshelm Quartz Monzonite magma has intruded and meta­ morphosed the Upper Paleozoic sediments of the Naco Group as well as the Lower Cretaceous sediments of the Bisbee Group. The metamorphism is of a contact metasomatic type to which the mineralogical and tex­ tural changes in the country rocks have been attributed. TABLE OF CONTENTS Page TABLE OF ILLUSTRATIONS....................................... vii INTRODUCTION.......................................... .. • • 1 Location and Accessibility .......................... 1 Puipose of Investigation ..............•• .......... 1 Method of Investigation ..... ....................... 3 Previous Work .................................... 3 Acknowledgments .................................... It GEOLOGIC SETTING .... ....................................... 6 PETROGRAPHY................................................... 7 Igneous Rocks .................................. 7 Swisshelm Quartz Monzonite ....... ........... 7 Aplite Dikes ................... 31 Pegmatites • • • ........ ............ 38 Quartz Veinlet i|0 Inclusions ............................... I4O Porphyritic Rhyolite Dikes .......... ...... 53 Andesite Porphyry............................ 57 Lanprophyric (spessertite) Dikes ......... 59 Metamorphic R o c k s .................................... 6l Metamorphosed Rocks of Upper Paleozoic Age • • • • 6l Metamorphosed Rocks of Cretaceous Age ....... 71 S T R U C T U R E ..................................................... 78 Structure of the Metamorphic Rocks ...................... 78 Structure of the Intrusive Mass ............ 78 VARIATION DIAGRAMS . ....................... 81 v vx Page FETROGENESIS............ ...................................... 86 Swisshelm Quartz Monzonite »•••••• •.<>••••• 86 Aplite, Pegmatite, and Quartz ............ 89 Inclusions ........................ 91 Metamorphic Rocks ............... 92 CONCLUSIONS ................ .. 96 REFERENCES........ ................ V '. V . • 98 TABLE OF ILLUSTRATIONS Page PI# 1# Geologic Map of the Swisshelm Quartz Monzonite . p0^ e. Fig. 1. Index Map . .......... • .o-... 2 Fig. 2. Photomicrographs of the Normal Facies ...... H Fig. 3. Photomicrograph of a Phenocryst from the Normal Facies ......................................... 12 Fig. It. Photomicrographs of the Altered Facies ....... 17 Fig. £. Photograph of an Outcrop of Quartz Monzonite .... 18 Fig. 6. Photomicrograph of the Fine-grained Facies . 20 Fig. 7. Photomicrograph of the Diorite Contact Sub-facies * 23 Fig. 8. Photomicrograph of the Syenite Contact Sub-facies • 26 Fig. 9. Photomicrograph of the Aplite Porphyritic Facies . 33 Fig. 10. Photomicrograph of the Aplite Graphic Facies • • • • 35 Fig. 11. Photograph of the Swisshelm Quartz Monzonite Inclusions ............................ ••••• Jjl Fig. 12* Photomicrographs of the Biotite-Orthoclase-rich Inclusions ................... 1*3 Fig. 13o Photomicrographs of the Chlorite-Flagioclase-rich Inclusions .................................... li$ Fig. 1U. Photomicrographs of the Biotite-Plagioclase-rich Inclusions ................... Fig. 15. Photomicrograph of the Muscovite-Potash Feldspar- rich Inclusions ................ 50 Fig. 16. Photomicrograph of the Rhyolite Central Facies . 54 Fig. 17. Photomicrograph of the Rhyolite Border Facies . 56 vii viii Page Fig. 18. Photomicrograph of the Andesite Porphyry ...... 58 Fig. 19. Photomicrograph of the Porphyroblastic Marble * . 61; Fig. 20. Photomicrograph of the Garnet Granofels ....... 6? Fig. 21. Photomicrographs of the Idocrase Granofels ...... 69 Fig. 22. Photomicrographs of the Homblende-Biotite Granofels .............. ........ 7k Fig. 23. Photomicrograph of the Homblende-Porphyroblastic Granofels .................... 76 Fig. 21;. Photograph of Eroded Joints and Fissures in the Quartz Monzonite ................. 80 Fig. 25. Generalized Marker Variation Diagram ......... 83 Fig. 26. Ternary Variation Diagram .............. 8I4. INTRODUCTION Location and Accessibility This thesis covers a portion of the Swisshelm Mountains which are located in Cochise County in the extreme southeast comer of Ari­ zona, twenty miles from the town of Douglas and the Mexican border, and thirty miles from the Arizona-New Mexico border. They extend from 109O30‘ to 10?°#' N latitude and from 31°30‘ to 33.°kO* W longi­ tude. The Swisshelm Mountains are easily accessible from ail sides via ungraded gravel roads. The area investigated is a portion of the northwestern part of the Swisshelm Mountains and lies on the western side of the range. It comprises approximately the southern three-fourths of Sec. lit. Sec. 23, the northern quarter of Sec. 26, and the eastern fourth of Sec. 15 and 22. The area is reached by a seven mile drive over a partially Improved road east from ELfrida (Fig. 1). Purpose of Investigation This investigation interprets the petrographic features and proposes a petrogenetic history for a quartz monzonite stock. The igneous rocks are intrusive into a series of Paleozoic and Mesozoic sediments which have been contact metamorphosed. The characteristics of these rocks will also be discussed. 1 2 ARIZONA SCALE » 1 INCH - 11*6 MILES ELFRIDA o DOUGLAS \ SCALE i 1 INCH - 2k MILES FIGURE 1 • INDEX MAP SHOWING THE AREA OF STUDY 3 Method of Investigation Mapping of rock features was carried out in the field and plotted on an enlarged U. S. G. S, topographic map of the Swisshelm Mountains Quadrangle. Macroscopic characteristics were noted in out­ crops and in hand specimens. Specimens were collected in the field at the stations shown on the specimen location map (Plate 1). About 300 thin sections were prepared and studied in the Laboratory under the polarizing microscope. Selected thin sections from the various facies of the quartz monzonite stock and the aplite dikes were stained to aid in the estimation of the percentage of K-feldspar pres­ ent. Modal analyses for the igneous rock types were made by the point count method, using a mechanical stage with a minimum grid in­ terval of 0.2 mm. Chemical compositions of the various facies of the quartz monzonite were calculated from their modal analyses by use of the tables given in Wahlstrom (1955). Photographs and photomicro­ graphs were taken to illustrate important features. Previous Work boring (I9I4.7) wrote a thesis on the geology and ore deposits of the Mountain Queen area of the northern Swisshelm Mountains to the northeast of the thesis area. Galbraith and boring (1951) studied the Swisshelm district (in Arizona Zinc and Lead Deposits. part 2)• Rogers

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